None of the model predictions are certain. There is a lot that science does not yet know, and wider social and economic trends will also affect the UK's vulnerability to the effects of climate change. These range from an ageing population – with greater vulnerability to extreme heat – to population growth and increasing household and industry demand for water, which is expected to be 5% higher by 2020 compared with today. With 13% of new homes built since 2000 constructed on floodplains (that's about 10,000–16,000 new homes a year), planning decisions are another factor that can worsen the UK's existing vulnerabilities.